The leaked report said that RBS’s Global Restructuring Group (GRG), a department ostensibly set up to help companies in trouble, mistreated many of its clients.

It found that some form of “inappropriate action”, such as interest charges being raised or unnecessary fees added, was taken by GRG in relation to 92% of viable firms.

RBS has denied systematically abusing its customers.

‘Fair and balanced’

An FCA spokesman said the regulator welcomed “further dialogue” with the Treasury Committee on providing assurance about the publication of the summary.

He added: “The FCA has committed to publishing a detailed summary of the GRG report.

“To provide assurance on the summary, we previously asked an independent external counsel to confirm that it is a fair and balanced account of the full report’s findings.”

RBS’s Global Restructuring Group operated between 2005 and 2013 and at its peak handled 16,000 companies.

The unit would step in when businesses had missed a loan repayment, or had a notable dip in sales or profits, and was marketed as a turnaround specialist.

But the FCA report found that companies placed in the group had little chance of getting out of it. Only 10% returned to the main RBS bank intact.

At the end of 2014, 69% of firms were still in the successor to GRG.

Many of those businesses remained tied into complex loans with the bank in the form of derivatives linked to interest rates, from which it is often too expensive to leave.

RBS said it had apologised for previous mistreatment of some customers and had taken steps to put things right, including a new complaints process and an automatic refund of complex fees paid by these customers.